(CNN) -- Tuesday's round of primaries in seven states and Washington, D.C., is the last big event in the run-up to November's midterm elections. Hawaii holds the last nominating contest of this election cycle on Saturday.

Here are five things to watch for in Tuesday's races:

Ugliness in Delaware: The Tea Party Express poured money into the insurgent campaign of Christine O'Donnell. She is challenging longtime congressman and former Gov. Mike Castle, who is backed by the party establishment, in Delaware's Republican Senate primary. In some of the most vicious campaigning seen so far this year, Castle supporters have attacked O'Donnell, accusing her of defaulting on personal bills and not paying income taxes -- which she denies -- and calling her "delusional."

Establishment Republicans think they have a shot at picking up Vice President Biden's old Senate seat if Castle, a former governor, is their candidate, but don't stand a chance if O'Donnell wins the primary. But O'Donnell, who's been endorsed by former Alaska Gov. Sarah Palin, says the attacks have backfired and only intensified support around her.

The state GOP chairman said he had received death threats because of his support of Castle and had moved his family out of their home. O'Donnell condemned the threats.

Not as ugly to the north: Palin also endorsed a candidate in New Hampshire's GOP Senate primary but finds herself opposite other leading conservatives.

Palin is backing former state Attorney General Kelly Ayotte, whom she calls a "granite grizzly" in a robo-call that she recorded for the candidate. But other conservatives -- including local Tea Party groups, influential Sen. Jim DeMint and the state's largest newspaper, the Manchester Union Leader -- are backing Ayotte's opponent, Manchester attorney Ovide Lamontagne, who was the party's nominee for governor in 1996.

Ayotte was encouraged to get into the race by national Republicans and has been the frontrunner in the seven-candidate field. But recent polls show Lamontagne closing the gap.

On Monday, Joseph McQuaid, the conservative publisher of the Union Leader, blasted outsider influence on the race. In a front-page editorial, McQuaid wrote that Lamontagne "has rallied New Hampshire grassroots conservatives while Ayotte has attracted the big-name, let's-be-moderate types who want a candidate who will move to the squishy middle in November."

Rangel's toughest fight: Rep. Charlie Rangel has represented New York's 15th Congressional District for 40 years, but with a trial on ethics violations pending in the House, the 80-year-old congressman has attracted five challengers hoping to unseat him.

Rangel is expected to stand trial later this month on allegations of income tax and financial disclosure violations and that he used his influence to solicit donations for a college policy center which bears his name. The accusations forced him to step down from his post as chairman of the powerful House Ways and Means Committee.

Among those challenging Rangel are state Assemblyman Adam Clayton Powell IV, son of the scandal-plagued former congressman whom Rangel unseated in 1970.

Mayor's race has national implications: First-term Washington Mayor Adrian Fenty's tough re-election fight could carry implications for the national debate over education reform.

Fenty was elected in 2006 partly because of his promises to fix the district's ailing schools. He brought in an aggressive reformer as his schools chancellor, who closed schools and fired hundreds of teachers.

While the schools still lag behind national averages, test scores have improved. But Chancellor Michelle Rhee has drawn the enmity of local and national teachers' unions -- and that, in part, has the incumbent trailing D.C. City Council Chairman Vincent Gray in polls just before the vote.

Education reform advocates fear that a Fenty loss will dissuade politicians across the country from pursuing similar aggressive efforts.

• In New York, Tea Party-backed Carl Paladino is challenging party favorite Rick Lazio in the GOP governor's race. The winner will face Democrat Andrew Cuomo.

• In Wisconsin, there are competitive races in the Republican gubernatorial and Senate primaries.

• The Republican gubernatorial primary is the top race in Maryland.

• The Democratic primary in Massachusetts' 10th Congressional District got national attention over the weekend when Norfolk District Attorney Bill Keating, who is facing state Sen. Rob O'Leary, chased down a purse snatcher from a restaurant.